pH-responsive smart superwetting Fe foam for efficient in situ on-demand oil/water separation

Confronted with the increasing oily wastewater and oil leakage accidents, it is urgent to seek effective strategies to separate water/oil mixtures or clean spilt oil. In particular, the superwetting materials with special selective permeability have shown advantages in separating oil/water mixtures. Herein, Fe foams with switchable wettability were successfully fabricated via electrodeposition method and modification of mixed thiols. The smart Fe foam with pH-responsive wettability possessed selective separation performance for variety oil/water mixtures. In air, the superhydrophobic/superoleophilic foam worked in the oil-removing mode could allow the heavy oil to completely penetrate only by gravity, while retaining the water. After alkaline treatments, the water could spontaneously permeate through the superhydrophilic/underwater superoleophobic foam while preventing light oil from passing, belonging to the water-removing mode. After ten separation cycles, the separation efficiency of various oil/water mixtures still maintained not less than 98.5%. In addition, it also could achieve non-contact, remote control for oil–water separation. Meanwhile, the smart Fe foam possessed good mechanical durability, long-term stability and heat resistance. It is expected to provide a potential simple route to handle oil spills under various conditions and situations, which also is beneficial to expand the application of smart surface. Graphical abstract